.\" Copyright (c) 2021 Michael J. Karels
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.\" $FreeBSD$
.\"
.Dd December 8, 2021
.Dt GENET 4
.Os
.Sh NAME
.Nm genet
.Nd "Raspberry Pi 4 / BCM2711 Gigabit Ethernet controller driver"
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following lines in the
kernel configuration file:
.Bd -ragged -offset indent
.Cd "device miibus"
.Cd "device genet"
.Ed
.Sh DESCRIPTION
The
.Nm
driver supports the BCM2711 Ethernet controller
as found on the Raspberry Pi 4.
.Pp
The following features are supported in the
.Nm
driver in
.Fx :
.Pp
.Bl -item -offset indent -compact
.It
IP/TCP/UDP checksum offload for IPv4 and IPv6
.It
10/100/1000Mbps operation in full-duplex mode
.It
10/100Mbps operation in half-duplex mode
.El
.Pp
Note that the operation of transmit checksum offload is coupled
for IPv4 and IPv6; to disable it, both must be disabled even if both
address families are not in use.
.Pp
The
.Nm
driver supports the following media types:
.Bl -tag -width ".Cm 10baseT/UTP"
.It Cm autoselect
Enable autoselection of the media type and options.
The user can manually override
the autoselected mode by adding media options to
.Xr rc.conf 5 .
.It Cm 10baseT/UTP
Set 10Mbps operation.
The
.Xr ifconfig 8
.Cm mediaopt
option can also be used to select either
.Cm full-duplex
or
.Cm half-duplex
modes.
.It Cm 100baseTX
Set 100Mbps (Fast Ethernet) operation.
The
.Xr ifconfig 8
.Cm mediaopt
option can also be used to select either
.Cm full-duplex
or
.Cm half-duplex
modes.
.It Cm 1000baseT
Set 1000baseT operation over twisted pair.
Only
.Cm full-duplex
mode is supported.
.El
.Pp
The
.Nm
driver supports the following media options set with the
.Cm mediaopt
option to the
.Xr ifconfig 8
command:
.Bl -tag -width ".Cm full-duplex"
.It Cm full-duplex
Force full duplex operation.
.It Cm half-duplex
Force half duplex operation.
.El
.Pp
For more information on configuring this device, see
.Xr ifconfig 8 .
.Sh HARDWARE
The
.Nm
driver supports the Ethernet controller portion of the Broadcom BCM2711
on the Raspberry Pi 4 Model B and related systems.
It utilizes the BCM54213PE PHY.
.Sh LOADER TUNABLES
Tunables can be set at the
.Xr loader 8
prompt before booting the kernel or stored in
.Xr loader.conf 5 .
The following loader tunable variable is available, and is also
available as a read-only
.Xr sysctl 8
variable:
.Bl -tag -width indent
.It Va hw.genet.rx_batch
The maximum number of packets to pass to the link-layer input routine
at one time.
The default is 16.
.El
.Sh SYSCTL VARIABLES
The following variable is available as a
.Xr sysctl 8
variable:
.Bl -tag -width indent
.It Va hw.genet.tx_hdr_min
When the driver is given an output packet in a buffer chain
in which the first buffer contains only the Ethernet header,
the number of bytes of the packet to add to the Ethernet header
in the first buffer.
Certain packets may be lost if this value is too small.
The default value is 56, and is sufficient for the observed cases to date.
.El
.Sh DIAGNOSTICS
The
.Nm
driver has no diagnostics that are likely in normal operation.
However, when the
.Cm debug
option is set with
.Xr ifconfig 8 ,
most failures that cause packet loss in the transmit and receive paths
cause a cryptic diagnostic message naming the failure.
These messages generally make sense only when looking at the driver source.
.Sh SEE ALSO
.Xr altq 4 ,
.Xr arp 4 ,
.Xr miibus 4 ,
.Xr netintro 4 ,
.Xr ng_ether 4 ,
.Xr vlan 4 ,
.Xr ifconfig 8
.Sh HISTORY
The
.Nm
device driver first appeared in
.Fx 13.0 .
.Sh AUTHORS
The
.Nm
driver was written by
.An Mike Karels Aq Mt karels@freebsd.org .
Portions are derived from the bcmgenet driver in
.Nx
by Jared McNeill,
and parts of the structure and common code are from the awg driver
for the Allwinner EMAC by Jared McNeill.